The native-code compiler is only available on certain platforms.
It produces code that runs faster than the bytecode produced by
ocamlc, at the cost of increased compilation time and executable code
size. Compatibility with the bytecode compiler is extremely high: the
same source code should run identically when compiled with ocamlc and
ocamlopt.

It is not possible to mix native-code object files produced by ocamlc
with bytecode object files produced by ocamlopt: a program must be
compiled entirely with ocamlopt or entirely with ocamlc. Native-code
object files produced by ocamlopt cannot be loaded in the toplevel
system ocaml.

The ocamlopt command has a command-line interface very close to that
of ocamlc. It accepts the same types of arguments, and processes them
sequentially:

Arguments ending in .mli are taken to be source files for
compilation unit interfaces. Interfaces specify the names exported by
compilation units: they declare value names with their types, define
public data types, declare abstract data types, and so on. From the
file x.mli, the ocamlopt compiler produces a compiled interface
in the file x.cmi. The interface produced is identical to that
produced by the bytecode compiler ocamlc.

Arguments ending in .ml are taken to be source files for compilation
unit implementations. Implementations provide definitions for the
names exported by the unit, and also contain expressions to be
evaluated for their side-effects. From the file x.ml, the ocamlopt
compiler produces two files: x.o, containing native object code,
and x.cmx, containing extra information for linking and
optimization of the clients of the unit. The compiled implementation
should always be referred to under the name x.cmx (when given
a .o file, ocamlopt assumes that it contains code compiled from C,
not from Caml).

The implementation is checked against the interface file x.mli
(if it exists) as described in the manual for ocamlc
(chapter 8).

Arguments ending in .cmx are taken to be compiled object code. These
files are linked together, along with the object files obtained
by compiling .ml arguments (if any), and the Caml standard
library, to produce a native-code executable program. The order in
which .cmx and .ml arguments are presented on the command line is
relevant: compilation units are initialized in that order at
run-time, and it is a link-time error to use a component of a unit
before having initialized it. Hence, a given x.cmx file must come
before all .cmx files that refer to the unit x.

Arguments ending in .cmxa are taken to be libraries of object code.
Such a library packs in two files (lib.cmxa and lib.a)
a set of object files (.cmx/.o files). Libraries are build with
ocamlopt -a (see the description of the -a option below). The object
files contained in the library are linked as regular .cmx files (see
above), in the order specified when the library was built. The only
difference is that if an object file contained in a library is not
referenced anywhere in the program, then it is not linked in.

Arguments ending in .c are passed to the C compiler, which generates
a .o object file. This object file is linked with the program.

Arguments ending in .o, .a or .so (.obj, .lib and .dll
under Windows) are assumed to be C object files and
libraries. They are linked with the program.

The output of the linking phase is a regular Unix executable file. It
does not need ocamlrun to run.

Build a library (.cmxa/.a file) with the object files (.cmx/.o
files) given on the command line, instead of linking them into an
executable file. The name of the library can be set with the -o
option. The default name is library.cmxa.

If -cclib or -ccopt options are passed on the command
line, these options are stored in the resulting .cmxa library. Then,
linking with this library automatically adds back the
-cclib and -ccopt options as if they had been provided on the
command line, unless the -noautolink option is given.

-c

Compile only. Suppress the linking phase of the
compilation. Source code files are turned into compiled files, but no
executable file is produced. This option is useful to
compile modules separately.

-ccccomp

Use ccomp as the C linker called to build the final executable
and as the C compiler for compiling .c source files.

-cclib-llibname

Pass the -llibname option to the linker. This causes the given
C library to be linked with the program.

-ccoptoption

Pass the given option to the C compiler and linker. For instance,
-ccopt -Ldir causes the C linker to search for C libraries in
directory dir.

-compact

Optimize the produced code for space rather than for time. This
results in slightly smaller but slightly slower programs. The default is to
optimize for speed.

-dtypes

Dump detailed type information. The information for file x.ml
is put into file x.annot. In case of a type error, dump
all the information inferred by the type-checker before the error.
The x.annot file can be used with the emacs commands given in
emacs/caml-types.el to display types interactively.

-i

Cause the compiler to print all defined names (with their inferred
types or their definitions) when compiling an implementation (.ml
file). No compiled files (.cmo and .cmi files) are produced.
This can be useful to check the types inferred by the
compiler. Also, since the output follows the syntax of interfaces, it
can help in writing an explicit interface (.mli file) for a file:
just redirect the standard output of the compiler to a .mli file,
and edit that file to remove all declarations of unexported names.

-Idirectory

Add the given directory to the list of directories searched for
compiled interface files (.cmi), compiled object code files
(.cmx), and libraries (.cmxa). By default, the current directory
is searched first, then the standard library directory. Directories
added with -I are searched after the current directory, in the order
in which they were given on the command line, but before the standard
library directory.

If the given directory starts with +, it is taken relative to the
standard library directory. For instance, -I +labltk adds the
subdirectory labltk of the standard library to the search path.

-inlinen

Set aggressiveness of inlining to n, where n is a positive
integer. Specifying -inline 0 prevents all functions from being
inlined, except those whose body is smaller than the call site. Thus,
inlining causes no expansion in code size. The default aggressiveness,
-inline 1, allows slightly larger functions to be inlined, resulting
in a slight expansion in code size. Higher values for the -inline
option cause larger and larger functions to become candidate for
inlining, but can result in a serious increase in code size.

-linkall

Forces all modules contained in libraries to be linked in. If this
flag is not given, unreferenced modules are not linked in. When
building a library (-a flag), setting the -linkall flag forces all
subsequent links of programs involving that library to link all the
modules contained in the library.

-noassert

Turn assertion checking off: assertions are not compiled.
This flag has no effect when linking already compiled files.

-noautolink

When linking .cmxa libraries, ignore -cclib and -ccopt
options potentially contained in the libraries (if these options were
given when building the libraries). This can be useful if a library
contains incorrect specifications of C libraries or C options; in this
case, during linking, set -noautolink and pass the correct C
libraries and options on the command line.

-nolabels

Ignore non-optional labels in types. Labels cannot be used in
applications, and parameter order becomes strict.

-oexec-file

Specify the name of the output file produced by the linker. The
default output name is a.out, in keeping with the Unix tradition. If
the -a option is given, specify the name of the library produced.
If the -output-obj option is given, specify the name of the output
file produced.

-output-obj

Cause the linker to produce a C object file instead of an executable
file. This is useful to wrap Caml code as a C library,
callable from any C program. See chapter 18,
section 18.7.5. The name of the output object file is
camlprog.o by default; it can be set with the -o option.

-p

Generate extra code to write profile information when the program is
executed. The profile information can then be examined with the
analysis program gprof. (See chapter 17 for more
information on profiling.) The -p option must be given both at
compile-time and at link-time. Linking object files not compiled with
-p is possible, but results in less precise profiling.

Unix:

See the Unix manual page for gprof(1) for more
information about the profiles.

Full support for gprof is only available for certain platforms
(currently: Intel x86/Linux and Alpha/Digital Unix).
On other platforms, the -p option will result in a less precise
profile (no call graph information, only a time profile).

Windows:

The -p option does not work under Windows.

-pack

Build an object file (.cmx/.o file) and its associated compiled
interface (.cmi) that combines the .cmx object
files given on the command line, making them appear as sub-modules of
the output .cmx file. The name of the output .cmx file must be
given with the -o option. For instance,

ocamlopt -pack -o p.cmx a.cmx b.cmx c.cmx

generates compiled files p.cmx, p.o and p.cmi describing a
compilation unit having three sub-modules A, B and C,
corresponding to the contents of the object files a.cmx, b.cmx and
c.cmx. These contents can be referenced as P.A, P.B and P.C
in the remainder of the program.

Unix:

The -pack option is available only under platforms that
provide the GNU Binutils tools nm and objcopy.

-ppcommand

Cause the compiler to call the given command as a preprocessor
for each source file. The output of command is redirected to
an intermediate file, which is compiled. If there are no compilation
errors, the intermediate file is deleted afterwards. The name of this
file is built from the basename of the source file with the extension
.ppi for an interface (.mli) file and .ppo for an implementation
(.ml) file.

-principal

Check information path during type-checking, to make sure that all
types are derived in a principal way. All programs accepted in
-principal mode are also accepted in default mode with equivalent
types, but different binary signatures.

-rectypes

Allow arbitrary recursive types during type-checking. By default,
only recursive types where the recursion goes through an object type
are supported.

-S

Keep the assembly code produced during the compilation. The assembly
code for the source file x.ml is saved in the file x.s.

-thread

Compile or link multithreaded programs, in combination with the
system threads library described in chapter 24.

-unsafe

Turn bound checking off on array and string accesses (the v.(i) and
s.[i] constructs). Programs compiled with -unsafe are therefore
faster, but unsafe: anything can happen if the program accesses an
array or string outside of its bounds.

-v

Print the version number of the compiler and the location of the
standard library directory, then exit.

-verbose

Print all external commands before they are executed, in particular
invocations of the assembler, C compiler, and linker.

-version

Print the version number of the compiler in short form (e.g. 3.06),
then exit.

-wwarning-list

Enable or disable warnings according to the argument
warning-list. The argument is a string of one or several
characters, with the following meaning for each character:

enable/disable warnings for statements that do not have
type unit (e.g. expr1; expr2 when expr1 does not
have type unit).

U/u

enable/disable warnings for unused (redundant) match cases.

V/v

enable/disable warnings for hidden instance variables.

X/x

enable/disable all other warnings.

The default setting is -w Al (all warnings but labels enabled).

-warn-errorwarning-list

Turn the warnings indicated in the argument warning-list into
errors. The compiler will stop on an error as soon as one of these
warnings is emitted, instead of going on. The warning-list
is a string of one or several characters, with the same meaning as for
the -w option: an uppercase character turns the corresponding
warning into an error, a lowercase character leaves it as a warning.
The default setting is -warn-error a (all warnings are not treated
as errors).

-where

Print the location of the standard library.

Options for the IA32 architecture

Use the IA32 instructions to compute
trigonometric and exponential functions, instead of calling the
corresponding library routines. The functions affected are:
atan, atan2, cos, log, log10, sin, sqrt, and tan.
The resulting code runs faster, but the range of supported arguments
and the precision of the result can be reduced. In particular,
trigonometric operations cos, sin, tan have their range reduced to
[-264, 264].

Options for the Sparc architecture

The Sparc code generator supports the following additional options:

-march=v8

Generate SPARC version 8 code.

-march=v9

Generate SPARC version 9 code.

The default is to generate code for SPARC version 7, which runs on all
SPARC processors.

Executables generated by ocamlopt are native, statically-linked,
stand-alone executable files that can be invoked directly. They do
not depend on the ocamlrun bytecode runtime system.

During execution of an ocamlopt-generated executable,
the following environment variables are also consulted:

OCAMLRUNPARAM

Same usage as in ocamlrun
(see section 10.2), except that option l
is ignored (the operating system's stack size limit
is used instead) and option b is ignored (stack backtraces on
uncaught exceptions are not printed).

CAMLRUNPARAM

If OCAMLRUNPARAM is not found in the
environment, then CAMLRUNPARAM will be used instead. If
CAMLRUNPARAM is not found, then the default values will be used.

This section lists the known incompatibilities between the bytecode
compiler and the native-code compiler. Except on those points, the two
compilers should generate code that behave identically.

The following operations abort the program (via an hardware trap
or fatal Unix signal) instead of raising an exception:

stack overflow (except on IA32/Linux);

on the Alpha processor only, floating-point operations involving
infinite or denormalized numbers (all other processors supported by
ocamlopt treat these numbers correctly, as per the IEEE 754 standard).

In particular, notice that stack overflow caused by excessively deep
recursion is reported by most Unix kernels as a ``segmentation
violation'' signal.

Signals are detected only when the program performs an
allocation in the heap. That is, if a signal is delivered while in a
piece of code that does not allocate, its handler will not be called
until the next heap allocation.

The best way to avoid running into those incompatibilities is to never trap the Stack_overflow exception, thus treating it
as a fatal error both with the bytecode compiler and with the
native-code compiler.